This application relates to U.S. patent application Ser. No. 185,867, entitled "Ultraviolet Radiometer" by Telfair et al., filed Apr. 22, 1988.
While the subject invention is subject to a wide range of applications, it is particularly suited to display and analyze the two-dimensional intensity distribution across an ultraviolet (UV) laser beam. In particular, applications relating to beam viewing, near real-time intensity profilometry and quantitative diagnosis of laser beam quality are set forth.
As high fluence UV lasers move from the research laboratories into medical and industrial applications, there is an increasing need for better, more reliable diagnostic equipment to handle the high fluence and energetic photons. Better intensity uniformity and more repeatable pulse-to-pulse energy is demanded by such applications as photolithography and etching in the manufacture of semi-conductors, tissue ablation in opthalmology and angioplasty, and even routine material processing such as cutting and drilling. To develop these and other technologies, a more accurate masurement method is needed.
The conventional measurement techniques for intensity profile of laser radiation have been found to be inadequate for certain high power laser applications. Scanning systems using a wire, pinhole or slit (knife edge) are inadequate to measure intra pulse parameters. They are only usable with continuous lasers or for averaging high repetition rate pulsing systems. Linear arrays give only one line of data from each pulse. Two dimensional array camera systems with good resolution are the most useful for collecting data about intensity profiles, and they work well at the longer wavelengths.
When these technologies are applied to the high fluence, short pulse, UV excimer lasers, the energetic photons break chemical and atomic bonds and eject material by ablation at supersonic speeds. Hence, much of the energy is converted into chemical and translational energy and may be lost to the detection mechanism. In addition, the photons can be directly destructive to the detection system and cause it to change and/or shorten its lifetime.
By far, the most common technique for looking at laser beam shape and intensity structure is "burn" paper. One can expose a single pulse and get a two dimensional pattern. This pattern is really a single level threshold slice of the actual intensity profile. With papers of differing sensitivity, a multi-level slice profile of a laser beam (assuming the pulses are repeatable in shape and energy) can be constructed. These "burn" papers are, by their nature, very non-linear and even large intra pulse intensity variations in addition to the inter pulse variations can be missed.
A number of patents are directed to measuring the wavefront of a laser. These include U.S. Pat. Nos. 3,462,601; 3,549,886; 3,598,998; 3,680,965; 4,260,251; 4,376,892; 4,490,039; 4,602,272; and 4,670,646. However, none of these patents disclose the use of a plate of UV activated fluorescent material as with the present invention.
A description of various prior art systems was disclosed in a paper entitled "Characterization of UV Laser Beams Using Fluorescence", by Telfair et al., delivered at the Society of Photo-Optical Instrumentation Engineers (SPIE) on Jan. 15, 1988 in Los Angeles, Calif. and in articles entitled "Choosing And Using Laser-Beam-Profile Monitors", by Edwards, in Laser Focus/Electro-Optics, May, 1987, pgs. 76-84 and "Laser Beam Profiling The Automated Way", by Rypma, Photonics Sprectra, August, 1987, pgs. 67-74.
A material which has been found to be particularly useful in converting invisible UV radiation to visible fluorescent radiation is a rare earth doped garnet, Ce.sup.3+ : Y.sub.3 Al.sub.5 O.sub.12 (YAG). The ability of this material to fluoresce is described in an article entitled "CATHODOLUMINESCENT GARNET LAYERS", by J. M. Robertson, Thin Solid Films, 114 (1984) 221-240. The article, however, does not disclose the concept of measuring a high powered UV laser beam with an instrument incorporating the doped YAG material.
It is a problem relating to the present invention to provide an effective means for displaying and analyzing the intensity distribution across a high power, UV laser beam.
It is an advantage of the present invention to provide a beam intensity profilometer which obviates one or more of the limitations and disadvantages of the described prior arrangements.
It is a further advantage of the present invention to provide a beam intensity profilometer which displays and analyzes the intensity distribution across UV laser beams.
It is a still further advantage of the present invention to provide a beam intensity profilometer which analyzes the intensity distribution across UV laser beams in near real-time.
It is a yet further advantage of the present invention to provide a beam intensity profilometer which measures the total power and energy of a laser beam in addition to displaying the intensity distribution.
It is a still another advantage of the present invention to provide a beam intensity profilometer which is relatively inexpensive to manufacture and operate.
Accordingly, there has been provided a beam intensity profilometer which includes a component to produce a fluorescent emission distribution having a spatial distribution linearly proportional to the local inensity of an incident UV beam aimed on the fluorescent emission distribution component. Devices for observing and analyzing the spatial distribution of the fluorescence are operatively connected to the fluorescent emission distribution component. In a second embodiment, an instrument for both analyzing the spatial distribution of the UV beam as well as the power and energy of the UV beam is provided.
Other embodiments are disclosed incorporating mirrors for reflecting the fluorescent emission distribution component to the photosensitive surface of a camera.
The invention and further developments of the invention are now elucidated by means of preferred embodiments shown in the drawings.